Screw machine



United States Patent O 3,549,280 SCREW MACHINE Hans Linneken, Bottrop,Germany, assignor to Gutehoifnungshutte Sterkrade Aktiengesellschaft,Oberhausen-Sterkrade, Germany Filed Jan. 2, 1969, Ser. No. 788,511

Claims priority, application Germany, Jan. 3, 1968,

Int. Cl. F04c 29/10, 17/12 U.S. Cl. 418-21 6 Claims ABSTRACT OF THEDISCLOSURE A rotary screw compressor or pump, r helical vane compressor,includes a housing having an inlet deiined at one end of the compressorrotors and an outlet adjacent the Outlet end. The slide is connected toa pressure equalization piston which is charged by the exit or inletpressure of the pump medium in a direction opposite to the charging ofthe slide.

SUMMARY OF THE INVENTION This invention relates, in general, to theconstruction of a rotary compressor, and in particular, to a new anduseful compressor or pump having a displaceable slide for controllingits output.

Screw compressors or pumps are known which include a means for varyingthe output from two interengaging rotors. For example, they may includean adjustable tap opening which leads to the compressor discharge. Theworking spaces of the rotors, as dened by the peripheries of the rotorvanes or threads, can come into communication with this tap opening fora regulated period of time which is dependent upon the position of aslide which serves as a control member. Such a slide, which is movableor adjustable relative to the rotors, is subjected to forces in axialdirections which correspond to the variations of the charging on therespective ends of the rotor as determined by the inlet and outletoperating pressures of the machine. Since the end face of the slidewhich is charged with the outlet or discharge pressure cannot be formedin any desired small size and since the compression ratio of the screwcompressors should be as large as possible for economical reasons, theconsiderable axial forces which act on the slide may be disadvantageousand may result in unreliable operation of the control device.

In another known screw compressor machine having a slide which ismechanically actuated by a threaded spindle, the axial forces whichappear on the slide are compensated by a hydraulic system. Adisadvantage of such a construction is that the hydraulic pressurenecessary for the compensation has to be supplied by an additional pumpwhich acts constantly. Adaptation of such a system to the variable axialforces which are caused by the pressure variations or fluctuations, bothin the front and rear end of the machine, require additional means forthe adjustment of the equalization of compensation pressure. For thisreason, an integrated transmission cannot be built without blocking theoil supply pipe for the hydraulic system.

In another known screw machine, the drive of the slide is caused bymeans of a piston which is charged on one or two sides. The piston ishydraulically actuated and this construction requires a constantlycomplicated return or recycling of the oil flow in order to maintain apredetermined slide position.

In accordance with the invention, there is provided a construction whichincludes a control slide which is connected with a pressure equalizationpiston. The pressure ICC equalization piston is charged by the inlet ordischarge pressure of the medium being pumped and in a directionopposite to that at which the slide is charged. In this construction,the corresponding end faces of the slide and the pressure equalizationpiston are of the same size, or at least, almost the same size. Theslide and the pressure equalization piston are thus only charged by thethrough-put medium. No auxiliary energy is necessary and this means thatboth the quantity of the medium being pumped and also the pressure ratioof the machine can be charged without changing the axial thrustequalization of the slide.

Accordingly, it is an object of the invention to provide an improvedscrew compressor which includes a slide which is connected to a pressureequalization piston, the piston being charged by either the inlet or thedischarge pressure in a direction opposite to that in which the slide ischarged.

A further object of the invention is to provide a screw compressor whichis simple in design, rugged in construction and economical tomanufacture.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its Operating advantages and specic objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which there is illustrated and described a preferredembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING The only figure in the drawing is anaxial sectional view of a portion of a rotary compressor constructed 1naccordance with the invention.

DETAILED DESCRIPTION OF TH'E PREFERRED EMBODIMENT Referring to thedrawing, in particular, the invention embodied therein comprises acasing or housing 3 for a spiral lobe or screw compresor having an inletand an outlet or discharge 2 spaced axially and vertlcally therefrom.The compressor comprises a pair of rotors or lobes only one of which,rotor 4, is visible 1n the drawing. The rotors cooperate to draw air orother fluid inwardly from the inlet 1 and discharge it out through theoutlet or discharge 2. As indicated in repsect to the rotor 4, therotors are supported on axially spaced bearings 5 and 6 in the upperportion of the casing 3. Below the rotors there is located an axiallyadjustable slide 7 having a connecting rod portion 8 terminating in areception piece 9 for a pressure equalization piston 1l). The pressureequalization piston 10 is mounted in a guide cylmderll which can bedetached from the casing 3 by removing securing bolts 20, 20. The guidecylinder 11 is closed by a detachable cover 12 which mounts a driveelement or motor 13 for rotating a threaded spindle 14. The threadedspindle 14 is threadably engaged with the pres sure equalization piston10 and rotation of the spindle will eiect axial movement of the pressureequalization piston within the guide cylinder 11.

The pressure equalization piston 10, in accordance with the invention,is located opposite the end face of the slide 7 which is charged by thedischarge pressure. The end face of the pressure equalization piston 10which faces away from the slide 17 is located within the guide cylinder11 and communicates through bores 15 in the pressure equalization piston15 in the slide 7 to the inlet 'side so that the inlet pressure acts onthe pressure equalization piston 10 and on one end of the slide 7 in thedirection opposite to the outlet pressure which acts on the slide 7 andthe reception piece 9 at the location of the outlet 2.

In order to facilitate the mounting and removal of the pressureequalization piston 10, the reception piece 9 .which is connected withthis piston hasa slightly smaller diameter than the pressureequalization piston itself. The slide 7 alsohas a diameter which isequal to that of the reception piece '9 so that it is small enough to beremoved with the equalization piston to the end of the guide cylinderafter the cover 1'2 is removed.'

The construction of the slide and the pressure equalization is such thatthey are charged by the inlet or discharge pressure of the throughputmedium itself and in a manner such that the system is balanced. Noauxiliary medium is necessary for loading of the parts in order toovercome unbalancing forces. With the construction, both the quantity ofthe throughput medium and also the nominal or rate of pressure ratio of`the machine can be changedy without changing the axial thrust balance ofthe slide.

What is claimed is:

1. A compressor comprising a housing having an inlet opening and adischarge spaced from said inlet opening, cooperative rotor meansmounted in said housing between said inlet and said outlet for drawing amedium in through said inlet and discharging it out through said outlet,a slide mounted in said housing for axial movement `and having an endface communicating with said' inletand an opposite end facecommunicating with said outlet, said-slide being located between saidrotor and said outlet and being movable to vary the ow area lfrom,

said rotor to said outlet, a pressure equalization piston in sealingengagement with said housing and connected to and movable in the sameaxial directions of said slide, and means for communicating the side ofsaid piston opposite to said slide to said inlet.

2. A compressor, according to claim 1, wherein said housing includes aguide cylinder extension facing away from said slide, said pressureequalization piston being movable in said guide cylinder extension, saidmeans for communicating the side of said piston opposite to said 'slideto said inlet comprising a connecting rod extending from said slide tosaid pressure equalization piston and a through passage defined throughsaid pressure equalization piston, said connecting rod and said slide tocommunicate said inlet to the opposite side of said pressureequalization piston from said slide.

4. A compressor, according to claim 3, wherein said guide cylindercomprises a removable cylindrical extension of said housing.'

5. A compressor, according to c1aim 4, including a motor mounted on saidextension cylinder, a threaded spindle rotated by said motor, saidthreaded spindle being threadably engaged with said pressureequalization piston fork shifting said piston within said guidecylinder.

6. A compressor, according to claim 5, wherein said pressureequalization and said slide are connected together by'a connecting rod,said connecting rod, said pressure equalization piston and said slidehaving a through passage therethrough for communicating the inlet sideof said slide with the opposite side of said pressure equalizationpiston from said slide.

References Cited UNITED STATES PATENTS 1,922,639 `8/1933 Resner 230-1381,948,907 2/1934 Egli 230-138 2,079,375 5/ 1937 McCollum 103-120(A)2,331,127 10/l943` MacNeil 103-120(A) 2,477,003 7/ 1949 Paget 230-1383,045,447 7/ 1962 Wagenius 230-138 3,314,597 4/ 1967 Schibbye 230-1383,432,089 3/ 1969 Schibbye 230-138 MARK NEWMAN, Primary Examiner W. l.GOODLIN, A'ssi'stant Examiner Y U.S. C1. X.R. 4118-201

